The independence equations employed by Castles et al. (2006) and McDougall et al. (2005), have been used to provide evidence for a dual route model of reading. However, such reports have been limited to basic naming tasks. To test the robustness of previous claims, we examined the utility of the independence equation in predicting the regular word reading ability of normal reading adults in a lexical decision task. Participants were asked to read regular words (REGs; e.g., hint), exception words (EXCs; e.g., pint), non-words (NWs; e.g., bint) and pseudohomophones (PHs; e.g., pynt) and push a button based on whether the stimuli sounded like a real word. Both reaction time and accuracy rates were measured. Regression analyses were used to evaluate variance accounted for in actual REG reading performance given a predicted REG performance that was calculated from PHs and EXCs performance and the application of the independence equation. Results showed that both reaction time and accuracy measures could be used in the independence equation to accurately predict REG reading performance. This study provides further evidence for the mathematically independent relationship between the sight vocabulary and the phonetic decoding systems and support for the Dual Route Model of reading.